The present invention relates to the art of synthesis route of polymer composites, polymer nanocomposites, organic-inorganic hybrid material, using supercritical fluids as solvent. Polymer composite in the present invention is defined as a composite containing organic and inorganic parts. The present invention provides an environmentally benign chemical process for synthesis of polymer composites, wherein supercritical fluids acts as solvent. Under impregnation in supercritical fluids, the free volume of applied polymer is increased, allowing molecules or ions to enter for further reaction to generate polymer composites.
Scientists and engineers have been aware of the unique solvent characteristics of supercritical fluids (SCF) for more than 100 years, but it is only in the past three decades that SCF solvents have been the focus of active research and development programs especially in the area of polymer and polymer composites processing. A detailed summary of SCF solvents have been touted as candidate media for inorganic, organic, heterogeneous catalysis and homogeneous catalysis, and polymerization processes, and as environmentally preferable solvents for solution coatings and powder formation. For example, Kajimoto, Chem. Rev., 99 (2), 355-390, 1999 reveals the history of supercritical fluid scientific findings and technology development and discusses the effects of solvation in supercritical fluids on energy transfer and chemical reactions.
In Christopher et al., Chem. Rev., 99 (2), 565-602, 1999 a review of Phase Behavior of Polymers in Supercritical Fluid Solvents has been made. The choice of CO2 as an alternative solvent has a number of advantages. CO2 is environmentally benign, non toxic, non flammable, and easily recyclable. J. Jung and M. Perrut, J. Supercritical Fluids 20,179-219, 2001 describes a review of particles generation in supercritical fluid. As particle design is presently a major development of supercritical fluids applications, mainly in the pharmaceutical, nutraceutical, cosmetic and specialty chemistry industries, number of publications are issued and numerous patents filed each years.
In supercritical fluids, the applied polymer may result in large changes in the host polymer's surface and bulk morphology by swelling effect. For example, in Clarke et al., J. Am. Chem. Soc., 116:8621 (1994), supercritical fluid is used to impregnate polyethylene with CpMn(CO)3 using supercritical CO2 which acts to both solvate the CpMn(CO)3 and to swell the polyethylene, thus permitting the flow of CpMn(CO)3 into the free space created in the swollen polymer and into the free volume of the polymeric material.
Polymer composite in the present invention is defined as a composite containing organic and inorganic parts. Polymer composites have been widely used with success for a variety of applications. For example, U.S. Pat. No. 6,608,129 to Koloski et al. describes disclosed composites for applications as photoradiation shields and filters, electro-magnetic radiation shields and filters, antistatic layers, heterogeneous catalysts, conducting electrodes, materials having flame and heat retardant properties, components in the construction of electrolytic cells, fuel cells, and optoelectronic devices, and antifouling coatings is also described.
U.S. Pat. No. 5,706,064 to Fukunaga et al. disclose composites for applications as liquid crystal displayer, an organic-inorganic hybrid glass, which is subjected to patterning, to form a pixel electrode. U.S. Pat. No. 6,472,104 to Ulrich et al. disclose a process for preparing a solid organic-inorganic hybrid polymer electrolyte containing lithium ions, wherein polyalkylene oxide-containing polymer and a organic lithium salt is mixed to form a mixture. The product shows high strength conductivity and lithium transference values. Further, the product can be self-organized into nanometer scale plates and rods paving the way to making lithium conducting cables for batteries of nanometer size.
The principles of synthesis methods and application of polymer composites can be found in books such as Carrado, Kathleen A. Polymer-Clay Nanocomposites, in Advanced Polymeric Materials, Shonaike, Gabriel O. and Advani, Suresh G, Eds. CRC press, New York, 349-396, 2003; Vincenza et al. Review of Polymer Composites with Carbon Nanotubes, in Advanced Polymeric Materials, Shonaike, Gabriel O. and Advani, Suresh G, Eds. CRC press, New York, 397-438, 2003; W. Shing-Chung et al. Performance Synergism in Polymer-Based Hybrid Materials, in Advanced Polymeric Materials, Shonaike, Gabriel O. and Advani, Suresh G, Eds. CRC press, New York, 439-478, 2003.
Herein is a summary of the synthesis of polymer composites, generally organic polymer is mixed with inorganic part, or organic polymer is formed in inorganic part, or inorganic part formed in organic part. Always these synthesis methods take multiple steps for the final polymer composites.
There are several synthesis routes for polymer composites. FIG. 1-3 describes the general route. The most economic and simple way are mixing the organic part and the inorganic part. The polymer composites are generated either (1) by melting the inorganic part or organic part or both and then mixed into a mixture which was then cured, extracted, or dried, or (2) by dissolving either the organic polymer or inorganic part or both in a solvent, and then introduce one part to another part, and then evaporating the solvent to extract the polymer composites. The resulting polymer composites may have separate inorganic and organic domains, which range from nanometers to tens of micrometers in size. For example, U.S. Pat. No. 5,492,769 to Pryor et al. describes methods for embedding metal or ceramic materials such as diamond, silicon dioxide, aluminum oxide, cubic boron nitride, boron carbide, silicon carbide, silicon nitride, tantalum carbide, titanium carbide, titanium nitride, tungsten carbide, and zirconia alloys and at least one phase stabilization additive selected from the group yttrium, hafnium, calcium, magnesium, and cesium to polymeric materials improve scratch or surface wear resistance of substrates.
U.S. Pat. No. 6,608,129 to Koloski et al. describes methods of that organic polymers are blended with inorganic fillers to improve certain properties of those polymers or to reduce the cost of the polymeric compositions by substituting cheaper inorganic materials for more expensive organic materials.
Polymer composites can be obtained by organic polymer formed on inorganic part through polymerization. Usually a catalyst, which is required to be prepared and be employed to initiate polymerization, is required to synthesis for the inorganic part, then introducing monomers onto the inorganic particle supported catalyst, and polymerization is followed to get organic polymer insulated on the inorganic particles. For example, U.S. Pat. No. 5,334,292 to Rajeshwar et al. discloses one invention concerns an electronically conductive polymer film comprising colloidal catalytic particles homogeneously dispersed in an electronically conductive polymer.
U.S. Pat. No. 6,602,966 to Vargas et al discloses a process producing ethylene (co)polymer nanocomposites in a high pressure polymerization reactor. The process by which nanocomposites having organically modified clays incorporated and intimately dispersed therein involves polymerizing ethylene and one or more optional comonomers under high pressure polymerization conditions in the presence of an organic peroxide initiator and organically modified clay. Such synthesis route has been subjected to a number of academic studies such as, Guan, Z., J. Am. Chem. Soc.; (Communication); 2002; 124(20); 5616-5617; Boone, H. W. et al J. Am. Chem. Soc.; (Communication), 124(30), 8790-8791, 2002; Wieczorek, W. et al, Electrochimica Acta, Vol. 40 (13-14), October, 2251-2258, 1995; Das, N. C. et al., Journal of Applied Polymer Science, Volume: 80, Issue: 10, 16, 1601-1608, 2001.
Polymer composites can be obtained by inorganic polymer formed on or within organic polymer through polymerization. Sometimes a coupling agent required to add to the organic part to enhance interaction of organic part and inorganic part. For example, U.S. Pat. No. 6,034,151 to Moszner et al. discloses hydrolyzable and polymerizable silanes containing vinyl groups can be applied as coupling agent.
U.S. Pat. No. 5,773,489 to Sato describes disclosed dental inorganic-organic composite fillers used for dental restorative materials, wherein the surfaces of the particles are modified with a silane coupling agent. The spherical or spheroidal particles were obtained in situ by co-hydrolysis of metal alkoxides and organic functional group-containing metal alkoxides.
Hydrolysis is a traditional synthesis route to generate inorganic particles either in micro or nano meter size meter. Hydrolysis is also applied to synthesis of polymer composites when polymer is impregnated or applied into the solution. For example U.S. Pat. No. 6,159,539 to Schwertfeger et al. discloses a process for preparing organically modified aerogels, wherein the process of the invention comprises: a) introducing a siliceous lyogel or hydrogel, b) optionally subjecting the gel prepared in a) to complete or partial solvent exchange with an organic solvent, c) reacting the gel obtained in step a) or b) with at least one silylation agent, d) optionally washing the silylated gel obtained in step c) with an organic solvent, and e) drying the gel obtained in step c) or d) subcritically, which comprises reacting in step c) the gel obtained in step a) or b) with at least one chlorine-free silylation agent.
U.S. Pat. No. 6,608,129 to Koloski et al. discloses methods for synthesis of polymer composites, which include a polymer matrix having natural free volume therein and an inorganic or organic material disposed in the natural free volume of the polymer matrix are disclosed. The free volume of organic polymer is evacuated, and inorganic or organic molecules are infused into the evacuated free volume of the polymer matrix. The inorganic or organic molecules can then be polymerized under conditions effective to cause the polymerized inorganic or organic molecules to assemble into macromolecular networks. Use of the disclosed composites as photoradiation shields and filters, electromagnetic radiation shields and filters, antistatic layers, heterogeneous catalysts, conducting electrodes, materials having flame and heat retardant properties, components in the construction of electrolytic cells, fuel cells, and optoelectronic devices, and antifouling coatings is also described.
U.S. Pat. No. 4,584,365 to Jada et al. describes a process for the production of polymeric substances from metal alkoxides, wherein multiple steps were comprised: (a) reacting at least a monofunctional carboxylic acid and at least a monofunctional hydroxylated organic compound in the presence of a suitable esterification catalyst to yield water in situ, and thereafter; (b) adding to the reaction mixture in (a) above at least a divalent metal alkoxide in an amount sufficient to form the desired polymeric network of at least partially hydrolyzed metal alkoxide. This polymer composite is applied for coating materials.
U.S. Pat. No. 581,176 to Ducheyne et al. discloses incorporation of biological molecules into bioactive glasses. In the invention there reports the incorporation of biologically active molecules into the matrix of glass, in particular bioactive glass, using a sol-gel-derived process of production. Therein a sol-gel-derived process using hydrolysis of a phosphorous alkoxide with the silicon alkoxide precursor and calcium alkoxide. Biologically active molecules are incorporated within the matrix of the glass during production.
In the hydrolysis process, there can be one or two or multiple components. For example U.S. Pat. No. 5,412,016 to Sharp discloses one synthesis method of polymer composites. Polymeric inorganic-organic compositions are obtained by intimately mixing a hydrolyzable precursor of an inorganic gel of silicon, titanium, or zirconium with an organic polymer and with an organic carboxylic acid. Such compositions often are transparent, always have improved toughness, as compared with inorganic gels alone, and are believed to have a structure in which the organic polymer is entrapped in the inorganic gel in such an intimate manner that these two components cannot be separated from each other by physical means without destruction of the organic polymer.
Although the polymer composites are homogeneously mixed, they contain separate inorganic and organic phases on a macromolecular scale. These separate phases frequently causes the inorganic part's migration within and/or leaching out of the polymeric matrix. Therefore, the inorganic part of the polymer composites can be separated from the polymer matrix by further processes either chemically or physically. Consequently, this will limit the lifetime.
The conventional synthesis methods as described in FIG. 1-3 usually take multiple steps for the final products of polymer composites. Multiple steps usually have a number of drawbacks of high consumptions of time, labor and cost while producing a large amount of inorganic or organic wastes. In the light of the above, according to the conventional technology, one improved method for synthesis of polymer composites is presented in the present invention. In this patent, improvements have been made to reduce the number of synthesis steps, received organic polymer or inorganic particles are employed and modified for further application, which has been described in FIG. 4.